My ex and her husband have split up he is/was step-father to my 13yo son for about 9 years does he have any automatic rights to contact with my son? Can his mother grant this? If so can I object?

First, ANY question on law needs to include a general locale as laws vary by area.

Most areas don't allow step parents rights, but there are some situations where a step parent may continue to have some rights.

However, the mother can allow him contact if she wishes and I don't think you would have any grounds to object unless he poses a danger to the child.